Preparation of terpinen-1-ol-(4)



United States Patent US. Cl. 260-6315 4 Claims ABSTRACT OF DISCLOSURE Process for preparing terpinen-1-ol-(4) which comprises oxidizing terpinolene to form 1-methyl-4-isopropenylcyclohexene-l-hydroperoxide-(4) and reducing said hydroperoxide to terpinen-l-ol-(4).

The present invention relates to a process for the manufacture of a terpene derivative.

Terpinen-1-ol-(4), i.e. 1-methyl-4-isopropyl-cyclohexen- 1-ol-(4), is an important constituent of many essential oils.

The present invention provides a process for the manufacture of terpinen-1-ol-(4) by oxidizing terpinolene (i.e., 1-methyl-4-isopropylidene-cyclohexene-(1)) to l-methyl- 4-isopropenyl-cyclohexene-1-hydroperoxide-(4), and reducing the said hydroperoxide to form terpinen-1-ol-(4).

The first stage of the reaction may advantageously be carried out by photosensitized oxidation of terpinolene. Such an oxidation, with oxygen or an oxygen-containing gas (e.g. air) is known per se (for example from German specification No. 933,925) and would normally be expected to give rise to a mixture of hydroperoxides, since oxygen would be expected to attack both the tri-substituted endocyclic and the tetra-substituted exocyclic double bond (see G. O. Schenk et al., Liebigs Annalen 1953, 584, 192). The first stage of the process of the present invention is based on the observation that, up to the consumption of 1 mole of oxygen per mole of terpinolene, the exocyclic double bond is exclusively attacked to form the desired 1-methyl-4-isopropenyl cyclohexene-l-hydroperoxide-(4) in good yield. Thus, with the displacement of the tetrasubstituted exocyclic double bond into the 9,10-position of the para-menthane skeleton the oxygen takes up the tertiary position on carbon atom 4 of the para-menthane skeleton. As a by-product, a small quantity of a x-paratrimethylbenzyl alcohol is formed, stemming from the simultaneously occurring unsensitized autoxidation of terpinolene. The tri-substituted endocyclic double bond of terpinolene is not attacked if the reaction is discontinued as soon as 1 mole of oxygen per mole of terpinolene has been absorbed. The hydroperoxide resulting from the photo-oxidation may then be reduced according to the present invention in a manner known per se to the hydroxy compound.

The process of the photosensitized oxidation is performed in known manner and has been repeatedly described in the literature. Compare, for example, the article of G. O. Schenck and K. Gollnick in Forschungsberichte des Landes Nordrhein-Westfalen No. 1256, Westdeutscher Verlag, Cologne and Opladen [1963], and French specification No. 1,319,202. Thus, the photosensitized oxidation may be carried out, for example, in the presence of suitable dyestuffs as sensitizers, for example methylene blue, Rose Bengal, Sudan-G, chlorophyll, eosine, zinc tetraphenyl-porphine, dinaphthylene-thiophene, or thionine, with the use of artificial or natural light and of oxygen or an oxygen-containing gas, for example air. For this operation it is advantageous to use the starting material and sensitizer in the form of a soluice tion, for example, in an alcohol as solvent. Particularly suitable are alcohols containing 1 to 6 carbon atoms, preferably methanol, ethanol and/ or isopropanol.

The 1-methyl-4-isopropenyl-cyclohexene 1 hydroperoxide-(4) resulting from the photosensitized oxidation is then reduced in known manner to the corresponding alcohol. The reduction may be carried out, for example, with aqueous sodium sulphite solution or with triphenylphosphine or with an alkali metal-aluminum hydride, for example LiAlH The resulting alcoholthat is 1-methyl-4-isopropenylcyclohexen-1-ol-(4)-is finally converted into terpinen-lol-(4) by selective partial hydrogenation with hydrogen in the presence of a catalyst; the yield is quantitative.

In the group of known metallic hydrogenation catalysts there are especially suitable the relatively mildly acting catalysts, such as Raney nickel or Raney cobalt. When other conventional metal catalysts, such as palladium or platinum, are used, the desired selective hydrogenation is likewise achieved but these catalysts involve a greater risk of an excessive hydrogenation effect.

The hydrogenation can also be performed, in known manner in a solvent. Particularly suitable solvents are lower alcohols containing 1 to 3 carbon atoms. Methanol is preferred.

According to the invention the photosensitized oxidation is generally carried out at a low temperature, advantageously within the range from 10 to +30 C., but as a rule room temperature is used.

EXAMPLE 136 grams (1 mole) of terpinolene and 0.5 g. of Rose Bengal are dissolved in 500 g. of methanol and subjected to the known photo-oxidation at room temperature while eing irradiated with light and gassed with oxygen. When 1 mole of oxygen has been absorbed, the reaction is discontinued and the reaction mixture stirred dropwise into a solution of 300 g. of sodium sulphite in 60 0 ml. of water, while maintaining the reaction temperature between 0 and 10 C. On completion of the dropwise addition the temperature is raised to C. and the batch stirred on at this temperature for 3 hours. After cooling, the 1- methyl-4-isopropenyl-cyclohexen-1-ol-(4) formed is isolated by extracting the reaction solution with benzene. After distillation there are obtained g. of 1-methyl-4- isopropenyl-cyclohexene-1-ol-(4) which reveals the following constants: d =0.9574, n =1.4961, B.P. 72 C. (5 mm. Hg). This alcohol is dissolved in ml. of methanol and hydrogenated with hydrogen at room temperature under atmospheric pressure in the presence of 0.5 g. of Raney nickel. Yield: 85 g. of terpinen-1-ol-(4). d4 =0.9315, n =1.4799.

What I claim is:

1. A process for the manufacture of terpinen-1-ol-(4), which comprises oxidizing terpinolene to 1-methyl-4-isopropenyl-cyclohexene-l-hydroperoxide by contacting terpinolene with at most 1 mole of oxygen per mole of terpinolene at -10 to 30 C. in the presence of a photosensitizer and light, reducing the said hydroperoxide to 1- methyl-4isopropenyl-cyclohexene-1-ol-(4) by contacting said hydroperoxide witha member selected from the group consisting of aqueous sodium sulfite solution, triphenylphosphine and alkali metal aluminum hydride, and partially selectively hydrogenating the said 1-methy1-4-isopropenyl-cyclohexene-1-ol-(4) by contacting it with hydrogen in the presence of a catalyst selected from the group consisting of Raney nickel, Raney cobalt, palladium and platinum to form terpinen-l-ol-(4).

2. A process as claimed in claim 1 wherein the terpinolene is dissolved in an alkanol having from 1 to 6 carbon atoms.

3. A process as claimed in claim 1, wherein the photosensitized oxidation is carried out in the presence of a dyestuff sensitizer.

4. A process as claimed in claim 3, wherein the sensitizer is methylene blue, Rose Bengal, Sudan-G, chlorophyll, eosine, zinc tetraphenyl-porphine, dinaphthylene thiophene, or thionine.

References Cited 1,319,202 1/1963 France.

4 OTHER REFERENCES Kenney et a1.: Photosensitized Oxidation of Carromenthane (1963), reprinted from J. Org. Chem. 28 3509 (1963).

Fisher: Research on Utilization of Limonene in the Naval Stores Laboratory (1965 reprinted from The Citrus Industry Magazine (October 1965) Sirnonsen: The Terpenes, vol. 1, 2nd ed. (1953), pp. 274-278, QD 416-58.

LEON ZITVER, Primary Examiner I. E. EVANS, Assistant Examiner US. Cl. X.R. 

